Rain impact sensing proximity fuze

ABSTRACT

Apparatus for momentarily desensitizing a proximity fuze in response to an impact with a raindrop. A rain impact sensor located in the nose cone of the fuze generates an electronic cutoff signal when the fuze hits a raindrop while in flight. The impact with the raindrop may also generate a spurious firing signal which can cause the firing circuit of the fuze to prefunction. The cut-off signal generated by the rain impact sensor is amplified, stretched and delivered to the firing circuit to effectively blank out any spurious firing signal received therein. The rain impact sensor may be embodied by a piezoelectric crystal mounted in the nose cone of the fuze, or a mechanical switch for sensing the shock wave generated by the impact of the raindrop, or a capacitive measuring bridge circuit that becomes unbalanced in response to the impact of the raindrop. The spurious firing signal is delayed before it reaches the firing circuit in order that the cut-off signal generated by the rain impact sensor will reach the firing circuit prior to any such spurious firing signal.

United States Patent Williams et al.

RAIN IMPACT SENSING PROXIMITY FUZE Inventors: David Williams, Bethesda;George K. Lucey, Jr., Silver Spring, both of Md.

The United States of America as represented by the Secretary of theArmy, Washington, DC.

Filed: Oct. 30, 1970 Appl. No.2 90,211

US. Cl. l02/70.2 P; 102/70.2 R;

102/702 GA Int. Cl. F42C 13/00; F42C 11/02 Field of Search... 102/702 P,70.2 R, 70.2 GA

[56] References Cited UNITED STATES PATENTS 11/1966 Winston 102/702 R12/1968 Resnick et al. 102/702 R 11/1970 Juliano et a1 102/702 R [57]ABSTRACT Apparatus for momentarily desensitizing a proximity fuze inresponse to an impact with a raindrop. A rain impact sensor located inthe nose cone of the fuze generates an electronic cut-off signal whenthe fuze hits a raindrop while in flight. The impact with the raindropmay also generate a spurious firing signal which can cause the firingcircuit of the fuze to prefunction. The cut-off signal generated by therain impact sensor is amplified, stretched and delivered to the firingcircuit to effectively blank out any spurious firing signal receivedtherein. The rain impact sensor may be embodied by a piezoelectriccrystal mounted in the nose cone of the fuze, or a mechanical switch forsensing the shock wave generated by the impact of the raindrop, or acapacitive measuring bridge circuit that becomes unbalanced in responseto the impact of the raindrop. The spurious firing signal is delayedbefore it reaches the firing circuit in order that the cutoff signalgenerated by the rain impact sensor will reach the firing circuit priorto any such spurious firing signal.

7. Claims, 2 Drawing Figures RAN \MPACT PULQE SENSOR STRETCHER F\\Z\NG 8cuzcun' 'l.0 /'I.'Z /'2 4 NORMALFllZlNC: serum.

31GNAL COND\T\ONER DELAY 1. Field of the Invention This inventionrelates to proximity fuzes and, more particularly, to an arrangementwithin a proximity fuze for negating the effects of spurious firingsignals caused by impacts with raindrops while in flight.

2. Description of the Prior Art The reliability of many low cost,proximity fuzes decreases in the presence of rain. Fuzes willoccasionally prefunction because of the electrical and/or mechanicaleffects of an impact with a raindrop For example, a loop fuze hitting ahigh dielectric raindrop will shift frequency momentarily and mayproduce a firing signal. Additionally, the mechanical impact may involvemore than 100 g forces, thereby causing microphonism from which firingpulses may be generated. Certain types of fuzes may also beprefunctioned if they impact with charged raindrops. Previous attemptsto minimize these effects have been largely unsuccessful due to the highcost and complexity of incorporating the necessary circuitry withexisting fuze designs.

It is, therefore, a primary object of the present invention to provide arain impact sensing proximity fuze that minimizes the electrical and/ormechanical effects of a fuze hitting a raindrop.

It is another object to provide a simple and low-cost arrangement withina proximity fuze for negating the effect of spurious firing signals inthe fuze caused by impacts with raindrops while in flight.

A further object of the present invention is to provide a simple,low-cost arrangement for momentarily desensitizing a proximity fuze uponimpact with a raindrop that is easily incorporated into existing fuzes.

An additional object of the present invention is to provide a proximityfuze designed for optimum fair weather performance that contains a rainimpact inhibitor that does not affect normal fuze operation.

SUMMARY OF THE INVENTION Briefly, in accordance with the invention, arain impact sensing proximity fuze is provided for momen- BRIEFDESCRIPTION OF THE DRAWINGS The specific nature of the invention as wellas other objects, aspects, uses, and advantages thereof will clearlyappear from the following description and from the accompanyingdrawings, in which:

FIG. 1 is a block diagram of a circuit arrangement embodying the presentinvention; and

FIG. 2 illustrates typical wave forms generated in the circuit of FIG. 1in accordance with the teachings of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, therain impact sensing proximity fuze of the present invention isillustrated generally at 10. During normal operation a firing signal isgenerated at 20 when the fuze approaches a predetermined distance fromthe target. Such a firing signal is sensed by signal conditioner -22 toensure that it is of the proper band width and frequency. A small delay24 is provided in the firing signal path prior to its receipt in thefiring circuit 18. Upon the receipt of a proper firing signal, firingcircuit 18 initiates a detonator to function the explosive in the fuze.As hereinbefore described, when a raindrop or a series of raindropsstrikes the fuze while in flight, a spurious firing signal may begenerated at 20 and may possibly be passed through signal conditioner 22and delay 24 to firing circuit 18 and, if it be of sufficient durationand amplitude, will cause a prefunction of the fuze. Negating the effectof such spurious firing signals is a rain impact sensor 12 thatgenerates an electronic cut-off signal in response to the impact of thefuze with the raindrop. The cut-off signal generated thereby is passedthrough an amplifier l4 and a pulse stretcher 16 to firing circuit 18.The receipt in firing circuit 18 of the amplified and stretched cutoffsignal momentarily desensitizes firing circuit 18 so that any spuriousfiring signal generated at 20 will have no effect upon the firingcircuit.

A typical desensitizing situation that occurs within firing circuit 18is illustrated in FIG. 2 in which wave form 26 represents a spuriousrain pulse firing signal that was generated at 20 upon the impact of thenose cone of the fuze with a raindrop and was passed through signalconditioner 22 and delay 24 to firing circuit 18. The same raindropactivated rain impact sensor 12, which, for example, can be apiezoelectric crystal, and produced a cut-off signal that was amplifiedby amplifier l4 and lengthened by pulse stretcher 16 before being fed tothe gate circuit of the firing SCR within firing circuit 18. The cut-offsignal 28 is seen to have blanked out the effect of rain pulse firingsignal 26 within firing circuit 18. It is seen that rain impact sensor12 can sense abnormal flight conditions and desensitize the fuze beforethe firing circuit is affected by the spurious firing signal due to thedelay 24 in the normal firing signal path. Normal fuze action isrestored after sveral milliseconds and the remainder of fuze operationis as if no rain were present.

Rain impact sensor 12 may also be a quick acting, very sensitivemechanical switch mounted on or near the nose cone of the fuze so thatthe shock wave generated by the impact of the raindrop is sensed priorto attenuation. Such a switch would initiate an electronic circuit thatblanks firing circuit 18 for a predetermined time interval. Rain impactimpact sensor 12 may also take the form of a capacitive measuring bridgecircuit that becomes unbalanced in response to the impact of the nosecone of the fuze with a raindrop impacting near the sensor. A normalproximity firing signal will not be inhibited in the presence of rainsince the rain impact sensor generates a cut-off signal of limitedduration and only upon the impact of the fuze with a raindrop, which atmost can be a periodic but not continuous action. This approach toreducing the effects of rain is seen to be simple, low cost, and easilyincorporated into existing fuze designs, having no effect on normal fuzeoperation.

We wish it to be understood that we do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

We claim as our invention:

1. A rain impact sensing proximity fuze, comprising:

a. a firing circuit that initiates the detonation of said fuze;

b. proximity sensing means for delivering a firing signal to said firingcircuit; and

c. rain impact sensing means for momentarily desensitizing said firingcircuit against unwanted firing signals generated by said proximitysensing means upon the impact of a raindrop with said fuze.

2. The invention according to claim 1, wherein said rain impact sensingmeans comprises:

a. a rain impact sensor for generating an electrical cut-off signal inresponse to the impact of said fuze with a raindrop; and

b. means for conditioning said electrical cut-off signal recieved fromsaid rain impact sensor and for delivering a momentary inhibit signal tosaid firing circuit that renders said firing circuit inoperative wherebyany firing signal generated in response to the impact with the rain willbe prevented from activating said firing circuit.

3. The invention according to claim 2 wherein said proximity sensingmeans includes means for delaying the receipt of said firing signal bysaid firing circuit whereby said momentary inhibit signal reaches saidfiring circuit prior to the receipt therein of a firing signal.

4. The invention according to claim 3 wherein said conditioning meansincludes an amplifier and a pulse stretcher.

5. The invention according to claim 3 wherein said rain impact sensorcomprises a piezoelectric crystal mounted on the nose cone of said fuze.

6. The invention according to claim 3 wherein said rain impact sensorcomprises a mechanical switch for sensing the shock wave generated bythe impact of said raindrop.

7. The invention according to claim 3 wherein said rain impact sensorcomprises a capacitive measuring bridge circuit that becomes unbalancedin response to the impact of said raindrop.

1. A rain impact sensing proximity fuze, comprising: a. a firing circuitthat initiates the detonation of said fuze; b. proximity sensing meansfor delivering a firing signal to said firing circuit; and c. rainimpact sensing means for momentarily desensitizing said firing circuitagainst unwanted firing signals generated by said proximity sensingmeans upon the impact of a raindrop with said fuze.
 2. The inventionaccording to claim 1, wherein said rain impact sensing means comprises:a. a rain impact sensor for generating an electrical cut-off signal inresponse to the impact of said fuze with a raindrop; and b. means forconditioning said electrical cut-off signal recieved from said rainimpact sensor and for delivering a momentary inhibit signal to saidfiring circuit that renders said firing circuit inoperative whereby anyfiring signal generated in response to the impact with the rain will beprevented from activating said firing circuit.
 3. The inventionaccording to claim 2 wherein said proximity sensing means includes meansfor delaying the receipt of said firing signal by said firing circuitwhereby said momentary inhibit signal reaches said firing circuit priorto the receipt therein of a firing signal.
 4. The invention according toclaim 3 wherein said conditioning means includes an amplifier and apulse stretcher.
 5. The invention according to claim 3 wherein said rainimpact sensor comprises a piezoelectric crystal mounted on the nose coneof said fuze.
 6. The invention according to claim 3 wherein said rainimpact sensor comprises a mechanical switch for sensing the shock wavegenerated by the impact of said raindrop.
 7. The invention according toclaim 3 wherein said rain impact sensor comprises a capacitive measuringbridge circuit that becomes unbalanced in response to the impact of saidraindrop.